We propose to measure simultaneously from an in situ ileal loop the direction and extent of changes in the Starling forces under a variety of physiological challengers to the intestinal system. The forces measured are capillary hydrostatic pressure, lymph and plasma colloid osmotic pressures, lymph flow, capillary filtration coefficient and interstitial fluid pressure (implanted capsule). Additional parameters that are measured are intestinal blood flow, arterial and venous pressure, changes in blood pH and hematocrit and changes in the A/G ratios of both plasma and lymph fluid. These forces will be measured during perturbations in arterial and venous pressure, drug induced vasodilation, vasoconstriction and changes in capillary permeability, hemodilution resulting from infusions of fluids, glucose induced mucosal absorption and cholera induced mucosal secretion. The understanding of the changes in the forces and flows will contribute in establishing a basic working model of the intestine in states of health and disease.